Conventionally, a liquid crystal display device has been used in a variety of electronic devices such as a television set, a laptop computer, a desktop personal computer, a PDA (personal digital assistant), and a mobile phone. The liquid crystal display device has the advantages that it (i) is thinner and lighter than a CRT (Cathode Ray Tube) display device and (ii) consumes less electric power than the CRT (Cathode Ray Tube) display device because the liquid crystal display device can be driven by a lower voltage than the CRT (Cathode Ray Tube) display device.
Particularly, a liquid crystal display device employing TFT (Thin Film Transistor) elements (such a liquid crystal display device is called a TFT liquid crystal display device) achieves high display quality, because all pixels are switched over via respective TFT elements.
Meanwhile, it has become rapidly widespread in an electronic device such as a television receiver that a moving image is displayed by such a liquid crystal display device. Accordingly, the liquid crystal display device has been required to further increase a response speed of a liquid crystal display panel so as to achieve a moving image with higher quality.
In view of the circumstances, it is an OCB mode liquid crystal display device that has particularly attracted attention recently. The OCB mode liquid crystal display device (OCB panel) is generally configured such that: a liquid crystal layer is provided between two substrates which have been subjected to an alignment treatment so as to cause liquid crystal molecules to be aligned in a same direction in parallel with one another; wave plates are provided on surfaces of the respective two substrates; and polarization plates are further provided on the respective wave plates so that the polarization plates are in a crossed Nicols relation.
(Reverse Transition)
In a case where the OCB panel is employed in a normally white mode (NW mode), in which a black display is carried out while a high voltage is being applied and a white display is carried out while a low voltage is being applied, a voltage applied to the liquid crystal layer needs to be reduced to nearly a critical voltage (Vcr) between spray and bend orientations so that a white display is achieved with high transmittance.
Because of this, a bend-spray transition (reverse transition) sometimes occurred while the white display was being carried out, which allowed a display to be no longer properly carried out. Note that the bend-spray transition here means a phenomenon of the liquid crystal molecules, which once have been in a bend orientation state, again returning into a spray alignment state.
(High White Voltage)
In order to prevent the reverse transition, there has been proposed a variety of methods. One of the methods is a method of increasing a voltage, which is applied to the liquid crystal layer while the white display is being carried out in the normally white mode (such a voltage is called a white voltage), to a voltage sufficiently higher than the critical voltage (Vcr).
However, with this method of increasing the white voltage, it was difficult to achieve an OCB panel with high brightness, because of trade-off between the white voltage and brightness (see FIG. 9).
FIG. 9 is a graph showing a relationship between a voltage applied and transmittance in an OCB mode liquid crystal display device which is a normally white mode. Here, the word Vcr denotes the critical voltage between spray and bend orientations.
(Black Insertion)
There has been proposed, as another method for preventing the reverse transition, a method in which a signal is applied separately from an image signal so as to prevent a reverse transition (refer to Patent Literature 1).
Specifically, for example, there has been proposed a method of stably maintaining a bend orientation by inserting a black display once or more times per frame of each display image.